Active pixel sensor and imaging system having differential mode

Abstract

An active pixel imaging system and method to generate an differential output signal consisting of the differences in a viewed image between adjacent detected flames. A buffered electrical charge storage capacity of the active pixel sensor is utilized to provide a system with reduced complexity and hardware requirements. In the imaging system, when a particular active pixel sensor is activated it generates a voltage signal corresponding to a previous frame's detect light intensity before the pixel is reset to generate a voltage signal corresponding to a present frame's detected light intensity. A differential output circuit is used to generate a differential output signal based on these two generated voltage signals.

We claim: 
     
       1. A method for generating a differential output video signal corresponding to an image focused on a sensor array having rows and columns of active pixel sensors, each sensor capable of collecting electrical charge based on a detected light intensity and having a diffusion well capable of holding an amount of electrical charge, each diffusion well being buffered from electrical signals generated external to the sensor, the method comprising the steps of: sequentially activating each row of sensors for a period of time to achieve a desired detected frame interval;   detecting a first voltage potential at a diffusion node of each activated sensor, wherein each of the first voltage potentials correspond to collected charges held by the respective diffusion wells for the detected image at a corresponding immediate previous frame;   resetting the voltage potential of the respective diffusion nodes of the activated sensors to a predetermined voltage potential;   transferring electrical charges collected for a present frame's detected light intensity from the image by each activated sensor to corresponding diffusion wells with the respective sensors, the voltage potentials at the activated sensors' diffusion nodes changing from the predetermined voltage potential to second voltage potentials corresponding to the respective amounts of transferred electrical charges;   detecting the second voltage potentials at the diffusion nodes of the activated sensors; and   generating an output signal based on sequentially determining the difference between the detected first and second voltage potentials of the activated sensors, wherein the sequential activation of each row of sensors generates an output signal of sequential segments of the detected differences in the image at the corresponding pixel sensors between the previous and present frames.   
     
     
       2. The method of claim 1, wherein the step of generating the output signal further comprises determining the difference between the detected first and second voltage potentials in the activated sensor row using respective differential output circuits connected to the active pixel sensors in each column. 
     
     
       3. The method of claim 1 further comprising the steps of: storing the first voltage potential of each activated sensor in a respective one of a first plurality of charge-storage devices; and   storing the second voltage potential of each activated sensor in a respective one of a second plurality of charge storage devices, wherein the step of generating the output signal includes applying the respective voltage potentials in each of the first and second pluralities of the charge storage devices to a like plurality of subtractive signal combiners that sequentially generate the corresponding portions of the differential output signal.   
     
     
       4. The method of claim 3, wherein the step of generating the output signal further comprises determining the difference between the detected first and second voltage potentials of a corresponding activated sensor by using respective differential output circuits containing the charge storage devices and subtractive signal combiner for each sensor in a corresponding column. 
     
     
       5. The method of claim 1, wherein the steps of detecting the voltage potentials at the diffusion nodes comprise the step of detecting corresponding outputs of voltage-follower transistors connected to the respective diffusion nodes. 
     
     
       6. The method of claim 1 further comprising the step of performing motion detection based on the generated output signal. 
     
     
       7. The method of claim 1 further comprising the step of performing data compression based on the generated output signal. 
     
     
       8. A method for generating a differential output video signal corresponding to an image focused on an active pixel sensor array, each sensor capable of collecting electrical charge for a detected light intensity and having a diffusion well capable of holding an amount of electrical charge, each diffusion well being buffered from electrical signals external to the sensor, the method comprising the steps of: sequentially activating sensors in different portions of the array for a period of time to achieve a desired detected frame interval;   detecting a first voltage potential at a diffusion node of each activated sensor, wherein each of the first voltage potentials correspond to collected charges held by the respective diffusion wells for the detected image at a corresponding immediate previous frame;   resetting the voltage potential of the respective diffusion nodes of the activated sensors to a predetermined voltage potential;   transferring electrical charges collected for a present frame's detected light intensity from the image by each activated sensor to corresponding diffusion wells within the respective sensors, the voltage potentials at the activated sensors' diffusion nodes changing from the predetermined voltage potential to second voltage potentials corresponding to the respective amounts of transferred electrical charges;   detecting the second voltage potentials at the diffusion nodes of the activated sensors; and   generating an output signal based on sequentially determining the difference between the detected first and second voltage potentials of the activated sensors, wherein the sequential activation of the sensors in each portion of the array generates an output signal of sequential segments of the detected differences in the image at the corresponding pixel sensors between the previous and present frames.   
     
     
       9. The method of claim 8, wherein the step of sequentially activating sensors in different portions of the array comprises activating the sensors in corresponding sensor rows. 
     
     
       10. The method of claim 8, wherein the step of generating the output signal further comprises determining the step of the difference between the detected first and second voltage potentials in the activated sensor row using respective differential output circuits connected to a respective active pixel sensor in each of the portions of the array. 
     
     
       11. The method of claim 8 further comprising the steps of: storing the first voltage potential of each activated sensor in a respective one of a first plurality of charge-storage devices; and   storing the second voltage potential of each activated sensor in a respective one of a second plurality of charge storage devices, wherein the step of generating the output signal includes applying the respective voltage potentials in each of the first and second pluralities of the charge storage devices to a like plurality of subtractive signal combiners that sequentially generate the corresponding portions of the differential output signal.   
     
     
       12. The method of claim 11, wherein the step of generating the output signal further comprises determining the difference between the detected first and second voltage potentials of a corresponding activated sensor by using respective differential output circuits containing the charge storage devices and subtractive signal combiner for each sensor in a corresponding portion of the array. 
     
     
       13. The method of claim 8, wherein the steps of detecting the voltage potentials at the diffusion nodes comprise the step of detecting corresponding outputs of voltage-follower transistors connected to the respective diffusion nodes. 
     
     
       14. The method of claim 8 further comprising the step of performing motion detection based on the generated output signal. 
     
     
       15. The method of claim 8 further comprising the step of performing data compression based on the generated output signal. 
     
     
       16. A method for generating a differential output signal from an active pixel sensor corresponding to the difference in the detected light intensity of an image over first and second integration time periods, the sensor having a diffusion well capable of holding an amount of electrical charge based on an amount of detected light intensity by the sensor, the diffusion well being buffered from electrical signals external to the sensor, the method comprising the steps of: detecting a first voltage potential at a diffusion node of the active pixel sensor corresponding to a collected charge held in the diffusion well for the light intensity detected during the first integration period;   resetting the voltage potential of the diffusion node to a predetermined voltage potential;   transferring electrical charge collected for a present frame's detected light intensity from the image by the active pixel sensor to the diffusion well, the voltage potential at the diffusion node changing from the predetermined voltage potential to a second voltage based on the amount of transferred charge;   detecting the second voltage potential at the diffusion node; and   generating an output signal based on the difference between the detected first and second voltage potentials taken at the diffusion node for the first and second integration period.   
     
     
       17. The method of claim 16 further comprising the steps of: storing the first voltage potential in a first charge storage device after detecting the first voltage potential; and   storing the second voltage potential in a second charge storage device after detecting the second voltage potential, wherein the step of generating the output signal includes the step of applying the voltage potentials stored in the charge storage devices to a subtractive signal combiner which generates the differential output signal.   
     
     
       18. The method of claim 16, wherein the steps of detecting the voltage potentials at the diffusion nodes comprises the step of detecting an output of a voltage-follower transistor connected to the diffusion node. 
     
     
       19. An imaging system for generating a differential output video signal based on an image focused on the imaging system, the imaging system comprising: a plurality of active pixel sensors arranged into an array of rows and columns, each active pixel sensor being operable to generate a voltage at a diffusion node corresponding to detected light intensity by the sensor, each active pixel sensor being further operable to buffer the voltage potential present on the diffusion node from other signals generated external to the sensor;   a row decoder having a plurality of control lines connected to the sensor array, each control line being connected to the sensors in a respective column, wherein the row decoder is operable to activate the sensors in a row;   a plurality of differential output circuits, each differential circuit being connected to the respective sensors in a column, each differential circuit being operable to store first and second voltage signals received from the connected sensors and to selectively provide a difference sensor output signal to the common output line; and   a timing controller connected to the row decoder and each differential output circuit, wherein the timing controller is operable to cause each sensor row to be sequentially activated, and to cause the activated sensors to provide a voltage signal corresponding to a previous detected frame to the output circuits and then to provide a voltage signal corresponding to a present detected frame to the output circuits, and wherein the timing controller is further operable to cause the differential output circuits to sequentially provide the difference output signal to the common output line to generate the imaging system differential output signal.   
     
     
       20. The system of claim 19, wherein the differential output circuit comprises: first and second switches connected to the sensors;   first and second charge storage devices connected to respective first and second switches, wherein the switches are controlled by the timing controller to provide the first and second voltage potentials to the charge storage devices; and   a subtractive signal combiner having first and second inputs and a differential output, the first and second inputs being connected to the first and second charge storage devices, wherein the charge storage devices store the voltage signals for the previous and present frames which are provided to the signal combiner which generates the difference output signal.   
     
     
       21. The system of claim 20, wherein the differential output circuit further comprises: a third switch connected to the signal combiner output and the common output line, wherein the timing controller controls the third switch to close during the time the corresponding sensor differential output signal is to be provided to the output line.   
     
     
       22. The system of claim 20, wherein the charge storage devices are capacitors. 
     
     
       23. The system of claim 19, wherein the active pixel sensors employ a double-polysilicon structure. 
     
     
       24. The system of claim 19, wherein the timing controller and the row decoder are a single device. 
     
     
       25. An imaging system for generating a differential output video signal based on an image focused on the imaging system, the imaging system comprising: a plurality of active pixel sensors arranged in an array, each active pixel sensor being operable to generate a voltage at a diffusion node corresponding to detected light intensity by the sensor, each active pixel sensor being further operable to buffer the voltage potential present on the diffusion node from other signals generated external to the sensor;   means for sequentially activating sensors in different portions of the array for a period of time to achieve a desired detected frame interval;   a plurality of differential output circuits, each differential output circuit being connected to the respective sensors in a corresponding portion of the array, each differential circuit being operable to store first and second voltage signals received from the connected sensors and to selectively provide a difference sensor output signal to a system output; and   a timing controller connected to the activating means and each differential output circuit, wherein the timing controller is operable to cause the sensors in each array portion to be sequentially activated, and to cause the activated sensors to provide a voltage signal corresponding to a previous detected frame to the differential output circuits and then to provide a voltage signal corresponding to a present detected frame to the differential output circuits, and wherein the timing controller is further operable to cause the differential output circuits to sequentially provide the difference sensor output signal to the system output to generate the imaging system differential output signal.   
     
     
       26. The system of claim 25, wherein the array sensors are arranged into rows and columns. 
     
     
       27. The system of claim 26, wherein the activating means is a row decoder. 
     
     
       28. The system of claim 25, wherein each of the differential output circuits comprises: first and second switches connected to the sensors of the corresponding array portion;   first and second charge storage devices connected to first and second switches, respectively, wherein the switches are controlled by the timing controller to provide the first and second voltage potentials to the first and second charge storage devices for storing; and   a subtractive signal combiner having first and second inputs and a differential output, the first and second inputs being connected to the first and second charge storage devices, respectively, wherein the charge storage devices store the voltage signals for the previous and present frames which are provided to the signal combiner for generation of the difference output signal.   
     
     
       29. The system of claim 28, wherein each of the differential output circuits further comprises a third switch connected to the signal combiner output and the system output, wherein the system output is a common output line, and wherein the timing controller controls the third switch to close during the time the corresponding sensor differential output signal is to be provided to the output line. 
     
     
       30. The system of claim 25, wherein the active pixel sensors employ a doublepolysilicon structure. 
     
     
       31. The system of claim 25, wherein the timing controller and the activating means are a single device. 
     
     
       32. An active pixel sensor arrangement having a difference output signal comprising: an active pixel sensor being operable to generate a voltage at a diffusion node corresponding to detected light intensity by the sensor, the active pixel sensor being further operable to buffer the voltage potential present on the diffusion node from other signals generated external to the sensor;   means for activating the sensor for a period of time to achieve a desired detected frame interval;   a differential output circuit connected to the sensor and being operable to store first and second voltage signals received from the connected sensor and to generate the difference sensor output signal based on the stored voltage signals; and   a timing controller connected to the sensor and the differential output circuit, wherein the timing controller is operable to cause the sensor to provide a voltage signal corresponding to a previous detected frame to the output circuit and then to provide a voltage signal corresponding to a present detected frame to the differential output circuit, and wherein the timing controller is further operable to cause the differential output circuit to generate the difference output signal.   
     
     
       33. The sensor arrangement of claim 32, wherein the differential output circuit comprises: first and second switches connected to the sensor;   first and second charge storage devices connected to first and second switches, respectively, wherein the switches are controlled by the timing controller to provide the first and second voltage potentials to the charge storage devices for storing; and   a subtractive signal combiner having first and second inputs and a differential output, the first and second inputs being connected to the first and second charge storage devices, respectively, wherein the charge storage devices store the voltage signals for the previous and present frames which are provided to the signal combiner for generation of the difference output signal.   
     
     
       34. The sensor arrangement of claim 32, wherein the active pixel sensor employs a double-polysilicon structure. 
     
     
       35. The sensor arrangement of claim 32, wherein the timing controller and the activating means are a single device.